Ethanol is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulose materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulose material, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol for fuels or consumption. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for fuel use.
With regard to the use ethanol produced from fermentation, the International Monetary Fund observed in 2008 that such fuels accounted for 1.5% of the global liquid fuels supply that year, but represented nearly half the increase in food crop consumption, mainly due to the use of corn-based ethanol in the U.S. In 2011, 40% of the U.S. corn crop will go into the motor fuel pool. Moreover, this fact has been said to have played a role in the increase in food prices.
Anhydrous ethanol or substantially anhydrous ethanol is often preferred for fuel applications. Anhydrous or substantially anhydrous ethanol, however, is often difficult to obtain from conventional hydrogenation and separation processes. For example, the ethanol and water produced in conventional hydrogenation reactions may form a binary azeotrope. This azeotrope contains about 95% ethanol and about 5% water. Because the boiling point of this azeotrope (78° C.) is just slightly below that of pure ethanol (78.4° C.), an anhydrous or substantially anhydrous ethanol composition is difficult to obtain from a crude ethanol composition via simple, conventional distillation.
Conventional ethanol compositions formed by the above-identified processes contain impurities which must be removed. For example, U.S. Pat. No. 5,488,185 utilizes a petrochemical feed stock and relates to an ethene stream which contains ethane as an impurity or a propene stream which contains propane as an impurity that is hydrated with water vapor in the presence of a hydration catalyst to produce ethanol or isopropanol, respectively. After removal of the alcohol the gaseous product stream is subjected to adsorption, thereby producing an ethene-enriched stream or a propene-enriched stream. The ethene-enriched stream or the propene-enriched stream is recycled to the hydration reactor.
U.S. Pat. Nos. 5,185,481 and 5,284,983 relate to conventional fermentation methods for producing ethanol. The produced ethanol compositions comprise impurities such as methanol, acetaldehyde, n-propanol, n-butanol, ethyl acetate, 3-methylbutanol, diethyl ether, acetone, secondary butanol, and crotonaldehyde. These references also disclose separation methods for treating the crude ethanol aqueous solution with an extracting solvent comprising carbon dioxide in a liquid state or carbon dioxide in a super-critical state.
U.S. Pat. Nos. 5,445,716; 5,800,681; and 5,415,741 relate to separation methods for mixtures of ethanol and isopropanol. Ethanol is difficult to separate from isopropanol by conventional distillation or rectification because of the proximity of their boiling points. Ethanol can be readily separated from isopropanol by extractive distillation. Effective extractive agents are dipentene, anisole, and ethyl benzene. The mixtures in these references, comprise a significant amount of isopropanol, e.g., at least 21.5 wt. % isopropanol.
Also, U.S. Pat. No. 5,858,031 relates to a method for enhancing the visibility of a flame produced during free-burning of an aqueous alcohol-based fuel composition in air. The fuel includes between approximately 10% and 30% by volume of water, and between approximately 70% and 90% by volume of a mixture of alcohols including ethanol and isopropanol, the ethanol constituting between approximately 24% and 83% by volume of the fuel composition. The method includes providing an amount of isopropanol ranging between approximately 7% and 60% by volume of the fuel composition, in which the volume ratio of isopropanol to ethanol in the fuel does not exceed 2:1.
Although conventional processes may produce and/or purify ethanol compositions, these processes rely on petrochemical feed stocks or fermentation techniques to yield the ethanol compositions.
Therefore, the need exists for an ethanol production process that does not rely on petrochemical feed stocks, and does not utilize fermentation techniques, which can be used to produce ethanol/fuel blend compositions.